1. Technical Field
The present invention relates generally to oscillator circuits for high frequency sources, and more particularly to a differential resonant ring oscillator circuit using a ring oscillator topology to electronically tune the oscillator over multi-octave bandwidths
2. Background Art
The background art is aptly described in only a few relevant documents, which include patents issued to one of the inventors of the present invention; notably, U.S. Pat. No. 5,801,591 to Parrott, which teaches a multi-octave ferrite oscillator topology that utilizes transformer coupling to provide the proper phase shift in the feedback loop. A ferrite element is magnetically saturated to produce a magnetic resonance An active element provides real impedance and gain over a wide frequency range at an input port. The input port is electrically coupled to a first inductive coupling structure that is electrically coupled to an RF current source/sink, such as ground. The magnetic resonance in the ferrite element induces a current in the coupling structure which is amplified and shifted in phase 180 degrees by the active element. The output of the active element drives a second inductive coupling structure that closes a feedback loop and provides an oscillator output signal. The first inductive coupling structure, ferrite element, and second inductive coupling structure act as a transformer when tuned to a resonance, thus providing the proper phase shift and current gain.
Next, U.S. Pat. No. 5,959,513 to Parrott describes an improved coupling structure for a ferrite-based resonator. The structure includes a mounting rod and a ferrite sphere mechanically coupled to a substrate that provides support for a stiff coupling loop. The structure reduces differential movement between the sphere and the coupling loop, thereby reducing vibration-induced degradation of resonator performance. The support structure also allows controllable insertion, removal, and rotation of the resonating element with respect to the RF coupling element. The support structure may be mechanically coupled to the RF coupling element to further reduce differential motion between the resonating element and the RF coupling element.
U.S. Pat. No. 6,348,840 to Ezura et al. discloses a variable-tuned type YIG oscillator with reduced mechanical variations in the resonance circuit. An amplifier element, electrode, circuit pattern, and other devices of the oscillator circuit portion of a YIG oscillator are integrated on the front face of a semiconductor substrate by the monolithic microwave integrated circuit manufacturing technique. A coupling loop is formed as a thick film conductor shaped so as to surround at least a portion of the outer periphery of a YIG crystal ball on the semiconductor substrate having the amplifier element, electrode, circuit pattern and others formed thereon. A hole for positioning a YIG crystal ball at a predetermined position inside of the coupling loop is formed in the semiconductor substrate from the front surface of the substrate, and the YIG crystal ball is fitted and fixed in the hole.
Finally, see U.S. Pat. No. 4,988,959, to Khanna et al, which teaches a broadband YIG-tuned oscillator having both series and parallel feedback. The oscillator includes a transistor capable of driving a load coupled to a first port thereof; a reactive feedback element coupled to a second port of the transistor; a YIG resonator, including means for tuning a YIG crystal for resonance throughout a range of frequencies; and a coupling to couple the YIG resonator to both a third port of the transistor and to the first port of the transistor.
The foregoing patents reflect the current state of the art of which the present inventors are aware. Reference to, and discussion of, these patents is intended to aid in discharging Applicants' acknowledged duties of candor in disclosing information that may be relevant to the examination of claims to the present invention. However, it is respectfully submitted that none of the above-indicated patents disclose, teach, suggest, show, or otherwise render obvious, either singly or when considered in combination, the invention described and claimed herein.